1. Field of the Invention
The present invention relates to an uninterruptible switching regulator in which an AC-side RCC (Ringing Choke Converter) type switching circuit drives a secondary drive circuit for driving a load such as a computer board when the commercial AC power supply is operating normally, and in the event of an unexpected situation such as a power outage, the system is automatically switched over so that the secondary drive circuit is instead driven by a DC-side RCC (Ringing Choke Converter) type switching circuit, and more particularly relates to an uninterruptible switching regulator configured such that an iron core and a magnetic path is shared by the AC-side RCC type switching circuit, the DC-side RCC type switching circuit, and the secondary drive circuit that connect a high-frequency transformer, the result of which is that a switching operation is performed between the switching element on the primary side and the switching element on the tertiary side in the supply of DC output to the secondary drive circuit. The present invention further relates to an uninterruptible switching regulator for a wide variety of computer applications; for instance, it can be used with a commercial AC power supply alone, it can be used with an external DC power supply alone, it can be used for automotive applications, and it affords uninterrupted operation through the double input of a commercial AC power supply and an external DC power supply.
2. Description of the Related Art
In Windows 95, 98, and NT, Linux, and other such operating systems used in personal computers, if the AC input power supply is accidentally turned off all of a sudden or if a power outage occurs during OS operation, for example, a memory failure can occur on the hard disk or, in a worst case, the OS can be damaged, requiring professional help for restarting the computer, and there has been a tremendous need in recent years for a way to deal with this situation. FIG. 13 illustrates a common approach to this problem, in which a UPS (Uninterruptible Power Supply) is connected to the computer in series, ahead of the internal AC/DC switching power supply. Still, cost concerns often dictate the use of an inexpensive UPS, and because a device with low reliability is serially connected between the computer and the commercial power supply, there is actually an attendant drawback of lower reliability, extra space is required, and the cost is also proportionately higher. FIG. 14 illustrates another method, which is often used on the existing internal switching power supply side. This is often used as a POS (Point Of Sale) system in which the commercial AC power supply is used to charge a battery that works by floating operation with an AC/DC switching power supply, and a DC/DC converter with multiple outputs put together into an integral structure on this load side is used as an internal uninterruptible switching regulator. Demand for this has been on the rise of late, as personal computers are increasingly used for POS systems. As another application, this system is also frequently used as an electronic switching device in PBX apparatus, and as personal computers make inroads in this area as well, uninterruptible switching regulators are again being used.
An advantage to the system shown in FIG. 14 is that the circuit is simple, but drawbacks are poor efficiency (50 to 55%), larger size, higher cost, and greater energy consumption, which is a problem from a societal and environmental standpoint.
Poor efficiency is due to the fact that the AC/DC conversion switching power supply and the DC/DC converter are connected in series, so the overall efficiency is the product of multiplying the efficiency of the various power supplies.
For instance, when an AC/DC conversion switching power supply with an efficiency of 70% is connected in series with a DC/DC converter with an efficiency of 80%, multiplying the numerical values of the efficiency of the two produces an efficiency of 56%, and a drawback is that the apparatus must be larger in order to obtain a large output.
Another major drawback is that because the battery is connected to the ground terminal of the computer board that is the load, maintenance, it is difficult to facilitate maintenance, including battery management by providing the batteries of a plurality of computers separately outside and in common. Also, the present inventors have already commercialized an uninterruptible switching power supply of medium capacity (150 to 400 W), but when a small-capacity supply (40 to 100 W class) is produced with this medium capacity system, called a separately excited forward converter, the circuit becomes more complicated and there are more parts, which makes it difficult to keep the size compact and the cost low.
As personal computers have become smaller and lower in capacity in recent years, micro-ATX specifications, SFX specifications, and same-device power supply specifications with panel computers and the like have been published, and there is a need for smaller packages. A continuous output of approximately 100 W must be obtainable with a case size of 100 mm in width, 63.5 mm in height (thickness), and 125 mm in depth, and among multiple outputs, low voltage outputs of 5 V and 3.3 V require a capacity of 70 to 80 W, but since the efficiency of an ordinary RCC type switching power supply is only about 60%, 40 to 50 W is generally the limit with a low voltage output.
In light of the above, it is an object of the present invention to provide an uninterruptible switching regulator with which smaller size and lower cost can be achieved while the power supply efficiency is raised, which is accomplished by the effective utilization of an RCC type switching circuit.
In order to achieve the stated object, the uninterruptible switching regulator of the present invention is such that an AC-side RCC type switching circuit equipped with a switching element, which rectifies and converts into DC an AC voltage from a commercial AC power supply serving as the input source and then operates using the smoothed DC voltage as its input, is connected to the primary winding of a high-frequency transformer, there is provided an input voltage detection circuit that detects when the input voltage from the commercial AC power supply to the AC-side RCC type switching circuit drops below a set voltage, a secondary drive circuit for driving a load such as a computer board is connected to the secondary winding of the high-frequency transformer, a DC-side RCC type switching circuit equipped with a switching element, which is completely electrically insulated from the AC-side RCC type switching circuit and the secondary drive circuit and operates using a battery, an external DC power supply, or the like as its input source, is connected to the tertiary winding of the high-frequency transformer, there is provided high-speed switching means for switching at high speed the operation of the AC-side RCC type switching circuit and the DC-side RCC type switching circuit on the basis of the detection information from the input voltage detection circuit, when the input voltage detection circuit detects that the input voltage from the commercial AC power supply is at or above the set voltage, the operation of the DC-side RCC type switching circuit is halted and power is supplied to the secondary drive circuit by preferentially operating the AC-side RCC type switching circuit with an output command from the input voltage detection circuit, and when the input voltage detection circuit detects that the input voltage from the commercial AC power supply has dropped below the set voltage, power is supplied to the secondary drive circuit by operating the DC-side RCC type switching circuit and halting the operation of the AC-side RCC type switching circuit with an inverse output command from the input voltage detection circuit.
To obtain an output of, say, about 100 W, which is required for a micro-ATX power supply size of determined case size of 100xc3x9763.5xc3x97125 mm as mentioned above, or to meet the need for an uninterruptible switching power supply that is as compact as possible even when used for a panel computer or a one-box server that uses Linux or the like for its OS, the system of the present invention is used as the basis, in which the circuit type is RCC, these two RCC type circuits, namely, the AC-side RCC type switching circuit and the DC-side RCC type switching circuit, are controlled independently, and these two circuits and the secondary drive circuit are shared via a high-frequency transformer. The circuitry can be simplified by using a configuration in which the abovementioned two circuits are switched on the basis of detection information from a single input voltage detection circuit. Also, providing a high-speed switching means for performing operation switching at high speed prevents a drop in secondary output. With a structure such as this, despite the smaller size, efficiency can be raised to over 70% not only with commercial AC input, but also with battery input (including external serial input).
There is provided a comparative amplifying element with an internal reference voltage for keeping the DC output to the secondary drive circuit at a constant voltage, the photo-diode sides of two photo-couplers are connected to the output terminal of this comparative amplifying element, either serially or in parallel via a balance resistor, the photo-transistors of the two photo-couplers are disposed one in the AC-side RCC type switching circuit and the other in the DC-side RCC type switching circuit, the collector terminals of the two photo-transistors are connected to the feedback input terminals of a PWM control IC used to control the switching circuits, the emitter terminals of the two photo-transistors are connected to the ground terminal of the PWM control IC, there are provided two transistors whose collector terminals are connected to the collector terminals of the two photo-transistors and whose emitter terminals are connected to the emitter terminals thereof (including cases when there is a certain amount of impedance in the connection), the base terminals of the two transistors and the input voltage detection circuit are connected such that the output commands from the input voltage detection circuit can be transmitted to the two base terminals in a mutually inverted state, and an RCC partial resonance type control IC, or an IC having substantially the same function as said IC, or a control circuit having substantially the same function as said IC, is used as the PWM control IC.
When the input voltage from the commercial AC power supply is at or above the set voltage, the transistor connected to the feedback terminal of the PWM control IC of the DC-side RCC type switching circuit is turned on by an output command from the input voltage detection circuit, and one of the photo-transistors that serve as the feedback signal of the PWM control IC is short-circuited, thereby bypassing the feedback current and halting the oscillation of the PWM control IC, which halts the supply of power to the secondary drive circuit from the DC-side RCC type switching circuit.
Conversely, an OFF command from the input voltage detection circuit is given to the transistor connected to the feedback terminal of the PWM control IC of the AC-side RCC type switching circuit, so the photo-transistor connected in parallel with this transistor remains in an operating state, and the output of the PWM control IC is in an oscillating state, so the AC-side RCC type switching circuit performs a switching operation and power to the secondary drive circuit is supplied from this switching circuit.
When the input voltage from the commercial AC power supply drops below the set voltage, the output of the input voltage detection circuit is inverted, because the control transistor turns on, the photo-transistor controlling the feedback terminal of the PWM control IC of the AC-side RCC type switching circuit is halted, the transistor connected to the feedback terminal of the PWM control IC of the DC-side RCC type switching circuit is turned off, and the photo-transistor connected to this terminal is put in an operating state, the result of which is that the output of the PWM control IC is in an oscillating state, the DC-side RCC type switching circuit performs a switching operation, and power to the secondary drive circuit is supplied from this switching circuit.
By using an RCC partial resonance type control IC, or an IC having substantially the same function as this IC, or a control circuit having substantially the same function as this IC, for the PWM control IC as the means for raising the efficiency of the above-mentioned RCC system, there is a reduction in loss during switching, there is less switching noise, and it is easier to deal with EMI.
If the high-speed switching means comprises a high-speed insulated inverting amplifier consisting of a photo-coupler or the like for optically linking the two switching circuits by the photo-transistors provided to the DC-side RCC type switching circuit and the photo-diodes provided to the AC-side RCC type switching circuit, and a clamping Zener diode provided between the collectors and emitters of the photo-transistors, then high-speed response can be achieved without the photo-couplers having to have a super-high-speed structure.
Also, if these transistors are connected by Darlington connection to the emitter ends of the photo-transistors, diodes are serially connected in the forward direction to the collector side of these transistors, and the cathode sides of these diodes are connected to the feedback terminals of the PWM control IC, the forward voltage of the diodes can be utilized so that the feedback terminals of the PWM control IC will not be drawn too deeply into the ground (GND) potential, allowing even better high-speed response to be achieved.
There are provided two supply circuits for supplying voltage to the PWM control IC used in the DC-side RCC type switching circuit, one of the supply circuits is equipped with a first electronic switch that passes the DC voltage from the battery, external DC power supply, or the like through a starting circuit and closes only while charging current is flowing to a starting capacitor, the other supply circuit is equipped with a second electronic switch for supplying the DC-side PWM control IC with auxiliary voltage made by rectifying the induced voltage of the tertiary winding after the supply of DC voltage from the first electronic switch has been received and the high-frequency transformer is in an oscillating state, and there are provided shutdown processing means for performing shutdown processing by outputting a computer end command when the input voltage detection circuit detects that the input voltage of the commercial AC power supply has dropped below the set voltage, and switch-off means for switching the second electronic switch off and turning the DC-side switching element off by a command from the photo-couplers upon completion of the processing by the shutdown processing means.
After the above shutdown processing, the switching of the DC-side RCC type switching circuit can be halted to halt the supply of power to the secondary side, and the DC-side switching element can be made to double as a power switch, with which the DC-side RCC type switching circuit can be shut off to keep dark current caused by wasted discharge down to just a few micro-amps.
A resonance capacitor is connected to either the winding end portion of the primary winding or the winding end portion of the tertiary winding, and the secondary drive circuit is provided with a synchronous rectifying circuit in which two FET""s are connected in totem pole fashion to a DC/DC converter circuit that makes a low-voltage large-current output and a polymer semiconductor capacitor or a capacitor with substantially the same low equivalent serial resistance as a polymer semiconductor capacitor.
When an electrolytic capacitor is used as a smoothing capacitor provided to the secondary drive circuit in an RCC system, 5 V and 10 A is the limit, the equivalent serial resistance (ESR) of this capacitor becomes a problem, a large amount of heat is generated, and heat treatment and a service life of 5 to 7 years cannot be expected, so a polymer semiconductor capacitor or a capacitor with substantially the same low equivalent serial resistance as a polymer semiconductor capacitor (at the same size, the equivalent serial resistance (ESR) of an electrolytic capacitor is 1:5, so that of a polymer semiconductor capacitor is far lower, and when the permissible ripple current is compared, a permissible current that yields 5:1 is obtained) is employed, which affords better efficiency and a smaller size. The circuitry can be simplified by connecting the resonance capacitor to either the winding end portion of the primary winding or the winding end portion of the tertiary winding. This is because the primary winding and tertiary winding that make up the magnetic circuit are linked in an equivalent parallel state, so providing the resonance capacitor to just one allows the same action to be imparted to the other. Efficiency can be further enhanced by using a synchronous rectifying circuit in which the main output on the secondary side is set at +12 V, for example, and two FET""s connected in totem pole fashion are used as rectifying elements as the way of making two voltages, such as 5 V and 3.3 V, with a DC/DC converter that makes voltage by chopper method from this +12 V voltage.
The high-frequency transformer comprises an iron core, an inner secondary winding around the iron core, whose number of turns is substantially half the total number of turns of the secondary winding, a tertiary winding wound via an interlayer insulator around the outside of this inner secondary winding, a primary winding that is a high-voltage winding wound via an interlayer insulator around the outside of this tertiary winding, and an outer secondary winding around the outside of this primary winding, whose number of turns is the remainder of subtracting the number of turns of the inner secondary winding from the total number of turns of the secondary winding, the inner secondary winding, the tertiary winding, and the outer secondary winding are made from flat copper boards, and the winding width of the inner secondary winding, the tertiary winding, and the outer secondary winding is the same as the winding width of the primary winding made of round wire.
To minimize the lead inductance of the windings of the high-frequency transformer and the wiring inductance on the secondary side of the high-frequency transformer as above, flat copper plates are used for the secondary winding and tertiary winding, the secondary winding is divided into an inner secondary winding and an outer secondary winding, and these are disposed in a special way and made thick and short, which reduces parasitic inductance, reduces the range and amount of cross-boarding (the region where the drain current and voltage overlap) when the FET that is a switching element is turned off, and allows efficiency to be increased and noise reduced.